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C program to insert substring into a string

C program to insert a substring into a string: This code inserts a string into the source string. For example,if the source string is "C programming" and string to insert is " is amazing" (please note there is space at beginning) and if we insert string at position 14 then we obtain the string "C programming is amazing". In our C program we will make a function which performs the desired task and pass three arguments to it the source string, string to insert and position. You can insert the string at any valid position.

C program

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void insert_substring(char*, char*, int);
char* substring(char*, int, int);

int main()
   char text[100], substring[100];
   int position;
   printf("Enter some text\n");
   printf("Enter a string to insert\n");
   printf("Enter the position to insert\n");
   scanf("%d", &position);
   insert_substring(text, substring, position);
   return 0;

void insert_substring(char *a, char *b, int position)
   char *f, *e;
   int length;
   length = strlen(a);
   f = substring(a, 1, position - 1 );      
   e = substring(a, position, length-position+1);

   strcpy(a, "");
   strcat(a, f);
   strcat(a, b);
   strcat(a, e);

char *substring(char *string, int position, int length)
   char *pointer;
   int c;
   pointer = malloc(length+1);
   if( pointer == NULL )
   for( c = 0 ; c < length ; c++ )
      *(pointer+c) = *((string+position-1)+c);      
   *(pointer+c) = '\0';
   return pointer;

Download Insert substring program.

Output of program:
Insert substring c program