Arrays in C and Prime Numbers -
i need programming assignment, have done except 1 part! here assignment:
problem 1: string operations , data security: improve data security in transmission of data , information, dynamic character coding being practiced. modification of original characters can using first 8 prime members [1, 2, 3, 5, 7, 11, 13, 17]: first character enhanced 1; second character 2, third 3, .. 8th character 17. next 8 characters use prime numbers in reverse order 17..1, , decrease values. use total message of @ least 64 characters [in quantities of 8 characters] , repeat process of modifying 1-17 first 8; modifying 17 -1 next 8, , on. make own message. after message coded, decoding should done, restore original message. may want change lower case , upper case transitions well.
example: original message b c d. ….. normal ascii 65 66 67 68 …. prime numbers 1 2 3 5 …. enhanced ascii 66 68 70 73 …. coded message b d f ……
i'm having trouble printing out prime numbers without messing code afterwards such encoded , decoded ascii codes , encoded , decoded codes. code far: if me somehow great! appreciate it, thank you.
size_t x; int i, c; = 1; c = 0; char text[65]; int s[8] = {1, 2, 3, 5, 7, 11, 13, 17}; printf("enter line of text: "); // prompts user enter text fgets(text, 65, stdin); // reads input user printf("\noriginal message: "); for(x = 0; x < strlen(text); ++x) // loop print original message { printf("%c", text[x]); } // end // ascii code printf("\nascii code: "); for(x = 0; x < strlen(text) - 1; ++x) { printf("%d ", text[x]); } // prime numbers // issue here printf("\n\nprime numbers: "); for(x = 0; x <= 8 ; ++x) { if(c == 0) { if(i == 1) { printf("1 "); ++i; } else if(i == 2) { printf("2 "); ++i; } else if(i == 3) { printf("3 "); ++i; } else if(i == 4) { printf("5 "); ++i; } else if(i == 5) { printf("7 "); ++i; } else if(i == 6) { printf("11 "); ++i; } else if(i == 7) { printf("13 "); ++i; } else if(i == 8) { printf("17 "); ++c; ++x; } } if(c == 1) { if(i == 8) { printf("17 "); --i; } else if(i == 7) { printf("13 "); --i; } else if(i == 6) { printf("11 "); --i; } else if(i == 5) { printf("7 "); --i; } else if(i == 4) { printf("5 "); --i; } else if(i == 3) { printf("3 "); --i; } else if(i == 2) { printf("2 "); --i; } else if(i == 1) { printf("1 "); --c; } } // end outer if } // issue ends here for(x = 0; x < strlen(text) - 1; ++x) { if(c == 0) // outer if statement increasing { if(i == 1) // inner if statement { text[x] = text[x] + 1; ++i; } else if (i == 2) { text[x] = text[x] + 2; ++i; } else if (i == 3) { text[x] = text[x] + 3; ++i; } else if(i == 4) { text[x] = text[x] + 5; ++i; } else if(i == 5) { text[x] = text[x] + 7; ++i; } else if(i == 6) { text[x] = text[x] + 11; ++i; } else if(i == 7) { text[x] = text[x] + 13; ++i; } else if(i == 8) { text[x] = text[x] + 17; ++c; ++x; } // end if statement } // end outer if statement if(c == 1) // outer if statement decreasing { if(i == 8) { text[x] = text[x] + 17; --i; } else if(i == 7) { text[x] = text[x] + 13; --i; } else if(i == 6) { text[x] = text[x] + 11; --i; } else if(i == 5) { text[x] = text[x] + 7; --i; } else if(i == 4) { text[x] = text[x] + 5; --i; } else if(i == 3) { text[x] = text[x] + 3; --i; } else if(i == 2) { text[x] = text[x] + 2; --i; } else if(i == 1) { text[x] = text[x] + 1; --c; } } // end outer if } // end printf("\n\nencrypted message: "); for(x = 0; x <= strlen(text) - 1; ++x) { printf("%c", text[x]); } printf("\nencrypted ascii: "); for(x = 0; x < strlen(text) - 1; x++) { printf("%d ", text[x]); } c = 0; = 1; for(x = 0; x < strlen(text) - 1; ++x) { if(c == 0) { if(i == 1) { text[x] = text[x] - 1; ++i; } else if(i == 2) { text[x] = text[x] - 2; ++i; } else if(i == 3) { text[x] = text[x] - 3; ++i; } else if(i == 4) { text[x] = text[x] - 5; ++i; } else if(i == 5) { text[x] = text[x] - 7; ++i; } else if(i == 6) { text[x] = text[x] - 11; ++i; } else if(i == 7) { text[x] = text[x] - 13; ++i; } else if(i == 8) { text[x] = text[x] - 17; ++c; ++x; } // end if statement } // end outer if statement if(c == 1) { if(i == 8) { text[x] = text[x] - 17; --i; } else if(i == 7) { text[x] = text[x] - 13; --i; } else if(i == 6) { text[x] = text[x] - 11; --i; } else if(i == 5) { text[x] = text[x] - 7; --i; } else if(i == 4) { text[x] = text[x] - 5; --i; } else if(i == 3) { text[x] = text[x] - 3; --i; } else if(i == 2) { text[x] = text[x] - 2; --i; } else if(i == 1) { text[x] = text[x] - 1; --c; } // end inner if statements } // end outer if statements } // end printf("\n\ndecrypted message: "); for(x = 0; x < strlen(text); ++x) { printf("%c", text[x]); } printf("\ndecrypted ascii: "); for(x = 0; x < strlen(text) - 1; ++x) { printf("%d ", text[x]); } puts(" "); } // end main
characters represented numbers. example, ascii, z represented number 122. if add value new value (e.g. 122 + 17 = 139). new value may not valid ascii (e.g. 128 or larger), , might control code (e.g. 127 "delete" control character).
because values may no longer represent valid characters, can't print them characters. need print them values (e.g. for(x = 0; text[x] != 0; x++) { printf("%d ", text[x]); }).
worse, "signed char", addition can cause overflow, undefined behaviour in c. you'd need use different data type (e.g. unsigned char or uint8_t) ensure code has defined/expected behaviour.
also note long chain of "if .. else if ... else if" statements should "switch()" cases; more this:
switch(i) { case 1: text[x] = text[x] + 1; ++i; break; case 2: text[x] = text[x] + 2; ++i; break; ... } however; using int s[16] = {1, 2, 3, 5, 7, 11, 13, 17, 17, 13, 11, 7, 5, 3, 2, 1}; you'd able replace many lines of similar code this:
for(x = 0; text[x] != 0; x++) { text[x] += s[x % 16]); }
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